The disclosure of Japanese Patent Application No. 2002-245075 filed on Aug. 26, 2002, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a control system of an internal combustion engine installed in an automobile, or the like, and more particularly to a fail-safe control technology for controlling the intake air quantity of the engine by using a variable valve mechanism and a throttle mechanism.
2. Description of Related Art
In recent years, one type of internal combustion engines installed in automobiles, or the like, has been developed which is provided with an electronically controlled throttle mechanism and a variable valve mechanism. In this type of engine, the electronically controlled throttle mechanism is arranged to drive (i.e., open and close) a throttle valve by means of an actuator, and the variable valve mechanism is capable of changing at least one of the opening/closing timing, a working angle and a lift amount of each of intake valves and/or exhaust valves.
A known example of the above type of the internal combustion engine, as disclosed in, for example, U.S. Pat. No. 6,039,026, includes a throttle mechanism capable of driving (i.e., opening and closing) the throttle valve independently of the amount of depression of the accelerator pedal, and a variable valve mechanism capable of changing the opening/closing timing and/or lift amount of intake valves. When the engine operates at a low or middle load, the opening angle of the throttle valve is set to a large degree, and the intake air quantity is adjusted by controlling the closing timing and/or lift amount of the intake valves.
In the known engine as described above, if a failure occurs in the variable valve mechanism, it becomes difficult to control the intake air quantity of the engine to a target intake air quantity, resulting in deterioration in the driveability and the quality of exhaust emissions, which may make it difficult for the vehicle in which the engine is installed to continue running.
It is therefore an object of the invention to provide a control system of an internal combustion engine in which the intake air quantity is adjusted by using an electronically controlled throttle mechanism and a variable valve mechanism, which system enables a vehicle in which the engine is installed to run at least in a limp-home mode when a failure occurs in, for example, the variable valve mechanism.
To accomplish the above and/or other objects(s), there is provided according to the invention a control system of an internal combustion engine, comprising (a) a timing changing unit that changes opening and closing timing of an intake valve relative to rotation of an output shaft of the engine, (b) a working angle changing unit that changes a working angle of the intake valve, (c) a throttle mechanism including a throttle valve provided in an intake passage of the engine and an actuator that is operable to open and close the throttle valve, (d) an intake air quantity control unit that controls the timing changing unit, the working angle changing unit and the throttle mechanism so as to control an intake air quantity of the engine to a target intake air quantity, (e) a failure detecting unit that detects a failure of at least one of the timing changing unit, the working angle changing unit and the throttle mechanism, and (f) a fail-safe control unit capable of executing different fail-safe control processes corresponding to different forms of failures that can be detected by the failure detecting unit. When the failure detecting unit actually detects a failure, the fail-safe control unit executes a selected one of the different fail-safe control processes depending upon the form of the failure detected by the failure detecting unit.
The control system according to the invention is employed in the internal combustion engine that controls the intake air quantity by utilizing the timing changing unit capable of changing the opening and closing timing of the intake valve relative to rotation of the output shaft of the engine (which will be called xe2x80x9cengine output shaftxe2x80x9d), the working angle changing unit capable of changing the working angle of the intake valve, and the throttle mechanism including the throttle valve and the actuator for driving (i.e., opening and closing) the throttle valve. The control system of the invention is characterized by executing a fail-safe control process selected from different fail-safe control processes corresponding to different forms of failures, when a failure or failures occur(s) in at least one of the timing changing unit, the working angle changing unit and the throttle mechanism in the internal combustion engine.
In the internal combustion engine that controls the intake air quantity by utilizing the timing changing unit, the working angle changing unit and the throttle mechanism, if a failure or failures occur(s) in one or both of the timing changing unit and the working angle changing unit, it becomes difficult for the intake air quantity control unit to control the actual intake air quantity of the engine to the target intake air quantity. In this case, an error between the actual intake air quantity and the target intake air quantity becomes excessively large, which may make it difficult for the engine to continue operating.
In view of the above situation, when a failure or failures occur(s) in one or both of the timing changing unit and the working angle changing unit, the control system of the engine according to the invention causes the fail-safe control unit to execute a fail-safe control process selected depending upon the form of the failure(s). In this case, an otherwise possible increase in the error between the actual intake air quantity and the target intake air quantity is suppressed, and therefore the engine can easily continue operating.
Examples of the different forms of failures may include (1) the case where a failure occurs in the working angle changing unit, (2) the case where a failure occurs in the timing changing unit, and (3) the case where failures occur in the working angle changing unit and the timing changing unit.
In one embodiment of the control system of the invention, when the failure detecting unit detects a failure of the working angle changing unit, the fail-safe control unit controls the working angle changing unit so that the working angle of the intake valve becomes substantially equal to a predetermined angle, and controls the timing changing unit so that the opening and closing timing of the intake valve substantially coincides with opening and closing timing corresponding to the predetermined angle, while controlling the throttle mechanism so as to change an opening angle of the throttle valve according to the target intake air quantity. In this case, the opening and closing timing of the intake valve is controlled to the timing corresponding to the working angle (i.e., the predetermined angle) of the intake valve, and the opening angle of the throttle valve is controlled to a degree determined according to the target intake air quantity. With this arrangement, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
Here, the failure of the working angle changing unit may be in the form of a failure of a drive unit (hereinafter referred to as xe2x80x9cworking angle changing drive unitxe2x80x9d) for changing the working angle of the intake valve, or in the form of a failure of a sensor (hereinafter referred to as xe2x80x9cworking angle sensing unitxe2x80x9d) for detecting or sensing the working angle of the intake valve.
When the failure detecting unit detects a failure of the working angle changing drive unit, it becomes impossible to change the operating angle of the intake valve. In this case, therefore, the fail-safe control unit may stop control of the working angle changing drive unit, and may control the timing changing unit based on the working angle detected by the working angle sensing unit, while controlling the throttle mechanism so as to change the opening angle of the throttle valve according to the target intake air quantity.
With the above arrangement, the opening and closing timing of the intake valve is controlled to the timing corresponding to the actual working angle, and the opening angle of the throttle valve is controlled to a degree determined according to the target intake air quantity. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
When the failure detecting unit detects a failure of the working angle sensing unit, on the other hand, it becomes difficult to accurately control the working angle of the intake valve. In this case, therefore, the fail-safe control unit may fix a control value applied to the working angle changing drive unit to a predetermined value, and may control the timing changing unit so as to fix the opening and closing timing of the intake valve to predetermined timing, while controlling the throttle mechanism so as to change the opening angle of the throttle valve according to the target intake air quantity.
With the above arrangement, the working angle of the intake valve and the opening and closing timing of the intake valve are fixed to a predetermined angle and the predetermined opening and closing timing, respectively, and therefore the intake air quantity of the engine can be suitably adjusted by changing the throttle opening. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
In the above-described control process, the opening and closing timing of the intake valve to be established when the engine is in an idling state is preferably retarded with respect to the opening and closing timing of the intake valve to be established when the engine is in a non-idling state. This is because, if the opening timing of the intake valve is excessively advanced while the engine is in an idling state, the volumetric efficiency of the intake air may be reduced due to reverse flow of exhaust gas.
In the control system of the engine according to the invention, when the failure detecting unit detects a failure of the timing changing unit, the fail-safe control unit may control the timing changing unit so that the opening and closing timing of the intake valve substantially coincides with predetermined opening and closing timing, and may control the working angle changing unit and the throttle mechanism so that the intake air quantity of the engine becomes substantially equal to the target intake air quantity.
In this case, since the opening and closing timing of the intake valve is fixed to the predetermined timing, the intake air quantity of the engine can be adjusted by changing the working angle of the intake valve and the opening angle of the throttle valve. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
Here, the failure of the timing changing unit may be in the form of a failure of a drive unit (hereinafter referred to as xe2x80x9ctiming changing drive unitxe2x80x9d) for changing the opening and closing timing of the intake valve, or in the form of a failure of a sensor (hereinafter referred to as xe2x80x9ctiming sensing unitxe2x80x9d) for detecting or sensing the opening and closing timing of the intake valve.
When the failure detecting unit detects a failure of the timing changing drive unit, it becomes impossible to change the opening and closing timing of the intake valve. In this case, therefore, the fail-safe control unit may stop control of the timing changing drive unit, and may control the working angle changing unit so as to fix the working angle of the intake valve to a predetermined angle, while controlling the throttle mechanism so as to change the opening angle of the throttle valve according to the target intake air quantity.
In this case, since the working angle of the intake valve and the opening and closing timing of the intake valve are fixed to the predetermined working angle and predetermined opening and closing timing, respectively, the intake air quantity of the engine can be adjusted by changing the opening angle of the throttle valve. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
When the failure detecting unit detects a failure of the timing sensing unit, it becomes difficult to accurately control the opening and closing timing of the intake valve relative to rotation of the engine output shaft. In this case, therefore, the fail-safe control unit may fix a control value applied to the timing changing drive unit to a predetermined value, and may control the working angle changing unit so as to change the working angle of the intake valve according to the target intake air quantity.
In this case, since the opening and closing timing of the intake valve is fixed to predetermined opening and closing timing, the intake air quantity of the engine can be adjusted by changing the working angle of the intake valve. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
In the above-described control process, if the opening and closing timing of the intake valve is retarded relative to rotation of the engine output shaft, the closing timing of the intake valve may be excessively retarded from the bottom dead center of the suction stroke, and the combustion stability of the engine may be reduced. It is therefore preferable to fix the opening and closing timing of the intake valve to such timing that is advanced relative to rotation of the engine output shaft.
In the control system of the engine according to the invention, when the failure detecting unit detects failures of the working angle changing unit and the timing changing unit, the fail-safe control unit may control the working angle changing unit so that the working angle of the intake valve becomes substantially equal to a predetermined angle, and may control the timing changing unit so that the opening and closing timing of the intake valve substantially coincides with predetermined opening and closing timing, while controlling the throttle mechanism so as to change an opening angle of the throttle valve according to the target intake air quantity.
In this case, the working angle of the intake valve and the opening and closing timing of the intake valve are fixed to the predetermined working angle and the predetermined opening and closing timing, respectively, and therefore the intake air quantity of the engine can be adjusted by changing the opening angle of the throttle valve. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
Examples of different forms of failures occurring in the working angle changing unit and the timing changing unit may include (1) the case where failures occur in the drive unit of the working angle changing unit and the timing sensing unit of the timing changing unit, (2) the case where failures occur in the working angle sensing unit of the working angle changing unit and the drive unit of the timing changing unit, (3) the case where failures occur in the working angle sensing unit of the working angle changing unit and the timing sensing unit of the timing changing unit, and (4) the case where failures occur in the drive unit of the working angle changing unit and the drive unit of the timing changing unit.
When the failure detecting unit detects failures of the working angle changing drive unit and the timing sensing unit, it becomes impossible to change the working angle of the intake valve, and it becomes difficult to accurately control the opening and closing timing of the intake valve. In this case, therefore, the fail-safe control unit may stop control of the working angle changing drive unit, and fixes a control value applied to the timing changing drive unit to a predetermined value, while controlling the throttle mechanism so as to change the opening angle of the throttle valve according to the target intake air quantity.
In this case, since the working angle of the intake valve and the opening and closing timing of the intake valve are fixed to a predetermined working angle and predetermined opening and closing timing, the intake air quantity of the engine can be adjusted by changing the opening angle of the throttle valve. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
When the failure detecting unit detects failures of the working angle sensing unit and the timing changing drive unit, it becomes difficult to accurately control the working angle of the intake valve, and it becomes impossible to change the opening and closing timing of the intake valve. In this case, therefore, the fail-safe control unit may fix a control value applied to the working angle changing drive unit to a predetermined value, and may stop control of the timing changing drive unit, while controlling the throttle mechanism so as to change the opening angle of the throttle value according to the target intake air quantity.
In this case, since the working angle of the intake valve and the opening and closing timing of the intake valve are fixed to a predetermined working angle and predetermined opening and closing timing, the intake air quantity of the engine can be adjusted by changing the opening angle of the throttle valve. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to control the operation of the engine.
When the failure detecting unit detects failures of the working angle sensing unit and the timing sensing unit, it becomes difficult to accurately control the working angle and opening and closing timing of the intake valve. In this case, therefore, the fail-safe control unit may fix a control value applied to the working angle changing drive unit to a first predetermined value, and fixes a control value applied to the timing changing drive unit to a second predetermined value, while controlling the throttle mechanism so as to change the opening angle of the throttle valve according to the target intake air quantity.
In this case, since the working angle and the opening and closing timing of the intake valve are fixed to a predetermined working angle and predetermined opening and closing timing, the intake air quantity of the engine can be adjusted by changing the opening angle of the throttle valve. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
When the failure detecting unit detects failures of the working angle changing drive unit and the timing changing drive unit, it becomes impossible to change the working angle and the opening and closing timing of the intake valve. In this case, therefore, the fail-safe control unit may stop control of the working angle changing drive unit and the timing changing drive unit, and may control the throttle mechanism so as to change the opening angle of the throttle valve according to the target intake air quantity.
In this case, since the working angle and the opening and closing timing of the intake valve are fixed to a predetermined working angle and predetermined opening and closing timing, the intake air quantity of the engine can be adjusted by changing the opening angle of the throttle valve. Consequently, the error between the actual intake air quantity and the target intake air quantity is less likely or unlikely to increase, which makes it easy to continue the operation of the engine.
In the internal combustion engine that controls the intake air quantity by utilizing the timing changing unit, the working changing unit and the throttle mechanism, a failure may occur in the throttle mechanism.
The failure of the throttle mechanism may be in the form of a failure of a drive unit (hereinafter referred to as xe2x80x9cthrottle valve driving unitxe2x80x9d) for driving (i.e., opening and closing) the throttle valve, or in the form of a failure of a sensing unit (hereinafter referred to as xe2x80x9cthrottle opening sensing unitxe2x80x9d) for sensing or detecting the opening angle of the throttle valve.
When the failure detecting unit detects a failure of the throttle valve driving unit or the throttle opening sensing unit, it becomes difficult to accurately change the opening angle of the throttle valve. In this case, therefore, the fail-safe control unit may fix the opening angle of the throttle valve to a predetermined degree by stopping control of the throttle valve driving unit or fixing a control value applied to the throttle valve driving unit to a predetermined value, and may control the working angle changing unit and the timing changing unit according to the target intake air quantity.
In this case, the working angle and opening and closing timing of the intake valve are respectively controlled to those determined according to the target intake air quantity, while the opening angle of the throttle valve is fixed at a certain degree, thus suppressing an otherwise possible increase in the error between the actual intake air quantity and the target intake air quantity.
In the case where the opening angle of throttle valve is fixed at a relatively large degree, however, the actual intake air quantity may become excessively large as compared with the target intake air quantity. In this case, the fail-safe control unit may execute ignition retard control for retarding ignition timing and/or reduced-cylinder operation control for operating the engine with a reduced number of cylinders so as to control the torque of the engine. With this arrangement, the engine is able to continue operating, while at the same time the torque of the engine is prevented from being excessively large as compared with the required torque.